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Thread: osb and mold

  1. #1
    brenda Guest

    Default osb and mold

    A customer called us about a soft spot in their roof along their ridge, upon inspection of this we found that the OSB, Micro-Lam, and I-Joists are disintegrating and wet. Construction is a vaulted ceiling with a blown in fiber glass (possible bibs system) 4/12 pitch span to ridge 14’eight years old. No leaks in ceiling visible, no settling of insulation only when peeling the fiberglass shingles from the cap and defective area there was whitish mold, which permeates throughout the area of the ridge. I was amazed that the Micro-Lam strand ridge beam you could remove handfuls of it was so soft.
    My recommendation would be to remove existing roof structure and install scissor trusses with a vented roof design. This is a shock to the homeowner and large expense and the owner was wondering about it being a mold/ insurance claim, while I am thinking there may be a defective OSB and the Micro-Lam strand beam may be art of the blame. Any thoughts and opinions on this would be appreciated.

    Thank you, Brenda

  2. #2
    Michael OHandley Guest

    Default Re: osb and mold

    Hi Brenda,

    I doubt that defective OSB is the issue. The OSB will remain fairly water tight for about 80 to 90 days before it begins to absorb water. Even if the beams had gotten wet, the roof plane usually dries out during the construction process long before things are completely closed in.

    More likely, warm/moist air has been rising to the peak of that ceiling and then leaking into the ridge area where its been cooled to dewpoint, condensed on and soaked into the ridge beam and I-joists and propagated rot. From your description is sounds like poria-incrassata or one of its cousins.

    Another possibility - if it is vented with a ridge vent - is wind driven snow being blown back through the vent and then melting and soaking into everything in the area during the day when the sun is up. Does it snow where you are? Was that area vented? Is there recessed lighting installed in the ceiling or other openings through which air can leak into that ceiling/roof envelope?



  3. #3
    BradS Guest

    Default Re: osb and mold

    Just curious, but if the problem is from a source of warm/moist air, where would this come from? And does the cooling of the air take place in any particular season? This sounds like a pretty scary situation I would like to understand more about and not make the mistake of building.

  4. #4
    brenda Guest

    Default Re: osb and mold

    Thanks Mike for your quick response. The construction of the roof system is 9.25” I-joists with what looks to be a BIB insulation system completely filling the 9.25” deep bay. Only two ceiling fans electrical boxes go thru the sheet rock. No venting whatever in this roof section which is allowed by code here (South Dakota) if the insulation fills the entire cavity, sort of like a wall cavity but deeper. I feel bad for the customer who is a 74-year-old retiree (employee’s uncle) that will not have the funds to fix it if insurance does not cover it. Meanwhile, what should I do to stop it from getting worse if I have cover up the whole and walk away from the house permanently?


  5. #5
    rbisys Guest

    Default Re: osb and mold


    This problem also exists on conventional framing too.
    The laminates are prone to breaking down quicker than soild wood when exposed to a wet enviroment.

    The area of greatest concern is the north side of the roof, although it can affect the whole roof. The moisture from the house passes through the wood and condensates ao the sheathing. It can also draw moisture from the outside air. Depending on the particulars it can concentrate- ate the top. The FG is also contributing to the problem because a dew point forms and condensation continues as long as the dew point is present. The fibers can also become saturated holding the moisture in the wood above the 15% dryness limit.

    There is a method to build and super insulate so that this problem is eliminated and the BTU gain/loss is held to less than 5 BTU/hr/sf. Unfortunately Mike doesn't, and doesn't want to, understand this process and threatens to kick me off if I talk about it. So if you want to know how to do it rigrt, e-mail me.

    Thank you for considering my opinion.


  6. #6
    Michael OHandley Guest

    Default Re: osb and mold


    Sorry to be so long getting back. Sometimes the regular job keeps me pretty tied up.

    Brad, moisture can get into a roof plane by migrating through the finish and drywall, by passing through switches, outlets and fixture boxes and around windows and doors. I think the system described was a poor choice for that climate because it permits too much air movement within the ceiling cavity, and as rbisys points out air moving toward the outer surface cools to dewpoint and saturates everything.

    OSB is very high in the sugar and starches that mold considers to be a buffet, so I think using it in an unvented roof plane with this type of insulation was pretty iffy at best. Dense-packed cellulose with a layer of CPVC primer and airtight boxes would have been a smart choice here.

    Whether you can save any of this depends on how much of it is rotten and I don't see you being able to determine that without completely stripping off the roof and decking and sucking all of that spore contaminated insulation out. You might then be able to cut out and replace rotted sections of microlam and I-joists, reinforcing them with scabs and then saturate everything in sight with BoraCare and let things dry out.

    We constantly debate the pros and cons here of venting or not venting cathedral ceilings. I guess it all boils down to if you don't want to vent it you need to make darn sure the ceiling and wall planes beneath that cathedral ceiling are totally sealed, have non-permeable finishes, no recessed fixtures or non-airtight boxes and use an insulation that will all but eliminate air movement through the roof cavity. That's a lot of work, but if you don't want to do that, you'll need to plan for the ventilation that you'll need to remove the moisture that gets into the roof plane.

    Since you are in an extreme climate Brenda, you might check out Fred Lugano's site or shoot him an e-mail for some additional extreme cold tips. I don't have the URL off the top of my head, but I am sure that if you take a minute to do a google search on Fred's name you'll find his site.




    You need to understand something. It is not that I don't want to understand radiant barriers, it is that what I have read and heard about them hasn't convinced me that they are the answer to everything under the sun (pun intended) - which sometimes seems to be what you believe. I don't spend my days thinking about radiant barriers like you do, so obviously I am able to be a little more objective.

    From where I stand, I see that folks a whole lot smarter than me have done plenty of research on radiant barrier systems over the past 50 years and very few of them have turned into radiant barrier missionaries. Now, if you wish to believe that all of these folks crossed over to the dark side and were part of a conspiracy to prevent you and other radiant barrier installers from succeeding, than you are more than welcome to do just that......elsewhere.

    This is a dead horse. Let it go.

  7. #7
    rbisys Guest

    Default Re: osb and mold


    The problem is, YOU DON"T WANT TOP UNDERSTAND RBs becauser that would mean that you have to admit that have been specifing/recommending substandard insulation materials. You STILL HAVE NOT contacted the experts, the tests you have brought forth are flawed, and you don't recognize it because you don't have the knowledgeexperience to interpet them. Example. The Florida test you cited was a flawed test for the following reasons.
    The test was of a single layer material that was installed to the bottom of the rafters. That is not the most eficient way to install a retrofit RB. The best method is over the insulation. Second the test was not a test involving the comfort levels of REAl people, it was an exptrapulation of the reducerd energuy flow thru the ceiling, NOT AN ACTUAL MEASUREMENT. It did not explore the possible reduction in humidity levels and their effects.
    This is why the use of emissivity values are so important. The engineering data is based on known energy flows based on differnt delta"T" values. If you Know what the ceiling/all temp is vs the floor temp it is very easy to calculate the efficiency of various materials. Why do you think you don't see these values? It's because you can't mickey mouse the data. It's pure, stright forward, simple, math. Why confuse the publ;ic with simplicity when you can fool them with BS.

    This test and others like it, including tests from ORNAL are subject to the same problems. This is why I have advocated "installed condition tests for over 20 years". The other problem is that in most cases you don't know who backed the tests. The utility companies jhave been famous for there bringing forth "TESTS" from an independent lab test. These tests either minimize or make RB look useless.

    Lets look at the DOE web site that cites ORNAL tests. In one case they cite the Florida tests and then turn around and cite an Oklahoma test involving several homes and said RB were useless. If you accept the low Florida test results, how do you get basicly zero in Oklahoma?
    Another interesting DOE/ORNAL comment. Heat convects downward. Since when did the laws of nature change? And there are other examples.

    I talked to one of the people at the Florida Solar Enery and they are interested in the new method I have developed of installing RB. Why would they be interested if RBs didn't work.

    Why would a geodesic dome manufacturer start recommending RBs to their cudtomers after I showed them how to ionstall in a dome?
    The PATH test was computer generated.

    You said that I claimed a 90% savings. That's not true. I said that RBs are 95-97% eff in reflecting heat energy. This is the same numbers the RB industry publish. The the same in an ME handbook.

    Thank you for considering my opinion.

  8. #8
    alan abrams cpbd Guest

    Default Re: osb and mold

    whether or not the structure can be salvaged and decontaminated is one thing--but a relatively benign solution for an unvented cathedral (less radical than the scissors truss retrofit) would be to strip the roofing and install a layer of rigid foam insulation over the roof deck--and another layer of sheathing for new roofing. The additional insulation must be thick enough to keep the original sheathing above dewpoint. Someone (Dow, I think) makes a panel that's osb bonded to xps, (like an open faced version of a SIP) for this general purpose.


  9. #9
    brenda Guest

    Default Re: osb and mold

    Alan and Mike, thanks for your input
    George (rbisys) thanks for the opinion

    My possible solution at the present time is to peel back the damaged area and treat with boracare
    I thought about adding the insulation as Alan mentioned but would worry that moisture would still accumulate at the ridge also I have had bad experience with foam insulation and ants.

    I would build a vented roof over the existing roof
    1. Sleepers 1.5” fastened to existing structure
    2. Continuous soffit vents
    3. Ridge vent
    4. plywood for roof decking

    This way I believe there would air circulation to remove any of the condensing vapor.

    1. Would 1.5” inches be deep enough for air to circulate?
    2. would I need to insulate the ridge beam

    thanks again for your input

    ps the insurance adjuster said it was wind damage

  10. #10
    Glenn Mitchell Guest

    Default Re: osb and mold

    The standard here on the "wet" coast is to have a min. of 1.5" EACH WAY vented. That is.. the FG insulation should be 1.5" below the tops of the roof joists and the strapping provides a further 1.5" purpendicular to that. There should be no diaphragm between them (such as the existing plywood.)

  11. #11
    brenda Guest

    Default Re: osb and mold

    any inexpensive places to buy?
    $ 90 gallon seems high

  12. #12
    Michael OHandley Guest

    Default Re: osb and mold

    Hi Brenda,

    It's been over $100. a gallon here on Puget Sound for years.



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